Semileptonic decays of charmed mesons in the effective action of QCD

Within the framework of phenomenological Lagrangians we construct the effective action of QCD relevant for the study of semileptonic decays of charmed mesons. Hence we evaluate the form factors of D -> P(0^-) l^+ nu_l at leading order in the 1/N_C expansion and, by demanding their QCD-ruled asymptotic behaviour, we constrain the couplings of the Lagrangian. The features of the model-independent parameterization of form factors provided and their relevance for the analysis of experimental data are pointed out.Comment: 1+24 pages, 1 figure. Updated version. Conclusions unchanged. Accepted for publication in The European Physical Journal

Barter, Credit, and Welfare: A theoretical inquiry into the barter phenomenon in Russia

This paper develops a model to investigate the welfare implications of barter in Russia and other transition economies during the 1990s. We argue that barter is a welfare-improving phenomenon that acts as a defense mechanism against monetary instability. When firms react to tighter credit markets by switching to barter, the risk they face diminishes, allowing for a higher level of production.Barter, welfare, Russia, money, credit, payment system, interest rate

Form factors of radiative pion decays in nonlocal chiral quark models

We study the radiative pion decay pi+ -> e+ nu_e gamma within nonlocal chiral quark models that include wave function renormalization. In this framework we analyze the momentum dependence of the vector form factor F_V(q^2), and the slope of the axial-vector form factor F_A(q^2) at threshold. Our results are compared with available experimental information and with the predictions given by the NJL model. In addition we calculate the low energy constants l_5 and l_6, comparing our results with the values obtained in chiral perturbation theory.Comment: 22 pages, 1 figure. arXiv admin note: substantial text overlap with arXiv:1011.640

La Web. Herramienta de trabajo Colaborativo: ¿Experiencia en la Universidad de Carabobo?

Indudablemente la revolución de la tecnología de la información y comunicación (TIC) a través de las telecomunicaciones y la informática han cambiando los estilos de vida en esta sociedad del conocimiento. Esto llega a indicar que estas TIC están aquí, y están para perpetuar en el tiempo. Hoy día se convive con el gran desafió que representa el uso de estas TIC en ambientes educativos por ello la necesidad de preparar y actualizar al personal docente de nuestro sector educativo (escuelas, colegios, tecnológicos, universidades, e institutos educacionales) para soportar el reto que implica su implementación. La Web es una de las herramientas de estas tecnologías que inducen a implementar cambios importantes en el proceso de enseñanza aprendizaje, específicamente en el desarrollo de trabajos colaborativos. Esta es una estrategia de aprendizaje que se ha expandido en todas las áreas de conocimiento facilitando a todos los actores del proceso (docentes, estudiantes) a una alta interacción de información construyendo su propio aprendizaje. El presente trabajo muestra una experiencia del uso de la web como herramienta en el trabajo colaborativo en cursos de "Diseño de Material Computarizado" en pregrado y postgrado en la Universidad de Carabobo y que demuestran la efectividad en el aprendizaje significativo de los tópicos tratados. Se utiliza como estrategia metodológica la creación de un entorno virtual de aprendizaje con el uso de la plataforma nicenet y el desarrollo de páginas web por parte de cada uno de los participantes de los cursos.The revolution of communication and information technology (CIT) through the use of telecommunications and computers has changed the life style of this society of knowledge. This fact indicates that this CIT is here to prevail in time. Nowadays we live with the challenge of the use of this CIT in educational environments, thus the necessity to prepare and to update the teachers and professors within the educational field (schools, technical colleges, universities, educational institutes) to sustain the defiance its implementation implies. The web is one of this technology tools that induces us to carry out important changes in the teaching and learning processes, specifically in the development of cooperative work. This is a learning strategy that has spread to all areas of knowledge, providing the teachers and the students with a high information interaction which permits them to build their own knowledge. The present paper exposes an experience on the use of the web as a cooperative work tool in courses of "Computerized Material Design", at pre and post degree levels at Carabobo University, that shows the efficiency of such a tool to accomplish a significant learning. The methodological strategy employed includes the creation of a learning virtual environment which comprises the use of the nicenet platform and the development of web pages by each of the participants of the courses

Los políticos, la política y la hacienda : breve opúsculo

Copia digital. Valladolid : Junta de Castilla y León. Consejería de Cultura y Turismo, 2009-201

Magnetism and half-metallicity at the O surfaces of ceramic oxides

The occurence of spin-polarization at ZrO$_{2}$, Al$_{2}$O$_{3}$ and MgO surfaces is proved by means of \textit{ab-initio} calculations within the density functional theory. Large spin moments, as high as 1.56 $\mu_B$, develop at O-ended polar terminations, transforming the non-magnetic insulator into a half-metal. The magnetic moments mainly reside in the surface oxygen atoms and their origin is related to the existence of $2p$ holes of well-defined spin polarization at the valence band of the ionic oxide. The direct relation between magnetization and local loss of donor charge makes possible to extend the magnetization mechanism beyond surface properties

Model analysis of the world data on the pion transition form factor

We discuss the impact of recent Belle data on our description of the pion transition form factor based on the assumption that a perturbative formalism and a nonperturbative one can be matched in a physically acceptable manner at a certain hadronic scale $Q_{0}$. We discuss the implications of the different parameters of the model in comparing with world data and conclude that within experimental errors our description remains valid. Thus we can assert that the low $Q^2$ nonperturbative description together with an additional $1/Q^2$ term at the matching scale have a strong influence on the $Q^2$ behavior up to very high values of $Q^2$ .Comment: 6 pages and 3 figures. Contains a comparison with other models and additional reference